Curable polymeric resin materials are used for coating a variety of substrates to provide protection from mechanical damage and environmental degradation or corrosion. In many cases coating stacks including multiple different coating layers are utilized to provide different advantageous characteristics. Coating layers in these cases can include primer layers, which can act as an antioxidation coating as well as enhancing adhesion of subsequent coating layers, undercoats, and topcoats. The resulting coating stack provides a plurality of desired protective characteristics to the coated substrate including durability and resistance to environmental degradation and corrosion.
Polyurethane network polymers are a class of coating resin materials that are commonly used to coat substrates. Conventional polyurethanes are produced by reaction of polyols with isocyanates to produce isocyanate polyurethanes. However, isocyanates are generally toxic and competing side reactions during the polymerization can generate gas which can result in undesired porosity in the resulting coating layer. In addition, isocyante derived polyurethanes may have hydrolytically unstable chemical bonds rendering them susceptible to environmental degradation. Thus, efforts to produce polyurethanes without the use of isocyantes have received some attention.
One approach to nonisocyanate polyurethane network polymers includes formation of polyurethanes by reaction of cyclic carbonates with primary amines. However, processes for producing nonisocyante polyurethanes using this approach may result in resin coatings lacking durability, resistance to corrosion, yellowing upon extended exposure to UV light, and can generally require processing conditions for the preparation and curing of the polyurethane coating layers, such as high cure temperatures, that may prevent optimal utilization of this approach.